Overview

A scratchy woollen jumper, an irritating bug bite or an itch on your back that you can't scratch, we all know and have experienced that itchy feeling. Estimates suggest that we itch on average a whopping 97 times a day!¹ Are you feeling it now?

Itchy skin or pruritus (proo-ree-tus)² is a condition experienced by many. It can be very uncomfortable and is one of the most common reasons that people see their dermatologists (doctors who specialise in skin disorders).³ In cases of persistent itch, scratching may provide some temporary relief, however doing so may activate the itch-scratch cycle where the damage caused by scratching the skin can lead to further itching.³ Although itching, in general, isn’t usually a sign of anything serious, for people suffering from more persistent itching, understanding the cause of this is crucial for both their comfort and health.⁴ Here we will discuss the major causes of persistent itching and will look into when it may be time to see a doctor. 

Common causes of persistent itching

Dry skin, allergic reactions and skin conditions

Dry skin or xerosis is a condition experienced by many and arises when moisture is lost from the outer layers of the skin. It is this loss of natural oils and moisture that can lead to itchiness.⁵ Many factors contribute to the occurrence of dry skin including heat, ageing, harsh soaps and detergents, certain medical treatments, bathing too frequently and living in harsh environments such as cold, windy or low-humidity environments.⁵ Itching caused by dry skin is generally mild and can often be remedied at home with unperfumed moisturisers.⁴

Allergies are another cause of itchy skin. An allergy is when the body’s immune system overreacts to foreign substances or allergens that are generally harmless to most people. Common allergens include pollen, fungal spores, dust mites and pet dander.⁶ During allergic reactions, specific cells in our body called mast cells release a chemical known as histamine into the blood, this chemical plays a key role in inflammation and itching.³ Antihistamines are over-the-counter medications that can treat symptoms of itchy skin caused by allergies.⁴

Eczema, Psoriasis and Hives are all skin conditions that commonly cause patients to experience persistent itching.⁴ Eczema, also known as Atopic Dermatitis, is a condition that causes the skin to become dry, itchy and cracked. The characteristic dry and inflamed skin that accompanies an Atopic Dermatitis flare-up commonly affects the hands, inside of the elbows, backs of the knees as well as the face and scalp. Symptoms of Atopic Dermatitis can be triggered by things such as allergens, stress and the weather. Moisturising treatments and topical corticosteroids can be used to treat the symptoms of Atopic Dermatitis, with the latter generally being prescribed by a physician.⁷

Psoriasis is another skin condition commonly accompanied by persistent itching. The characteristic scales of flaky skin experienced by those with psoriasis are caused by the increased production of skin cells and lead to the itching sensation. Psoriasis can be diagnosed by your GP, who will also advise on the correct treatment course to follow.⁸ Hives (urticaria) is another skin condition that manifests as an itchy rash and is often caused by a trigger such as allergens, food, weather etc, which causes histamine to be released in the body and a rash to occur. Hives will often go away on their own but a pharmacist or GP may be able to help with persistent cases.⁹

Systemic causes of persistent itching 

Whilst disturbances to the skin provide an obvious explanation as to why you may be feeling persistent itching, conditions affecting your body internally such as liver or kidney disease may pose as another explanation for itching symptoms. 

Liver disease is characterised by the deterioration of the liver accompanied by its scarring and dysfunction. There are many types and causes of liver disease and interestingly one of the symptoms people with liver disease experience is persistent itching.10 Itching experienced by those with liver disease is believed to be caused by the accumulation of bile salts.¹⁰ Bile salts are made in the liver and function to help digest food in the gut but during liver disease, they may accumulate under the skin.¹¹

Similar to liver disease, chronic kidney disease is also recorded to cause itching symptoms in patients. Uremic pruritus is the medical term for itching associated with chronic kidney disease. The exact mechanism that causes this itching is unknown but the skin dehydration, systemic inflammation and immune dysfunction that are seen in kidney disease may provide an explanation. Itching affects many with late-stage kidney disease, causing significant discomfort, interrupting sleep and generally affecting quality of life.¹²

Thyroid conditions including hypothyroidism and hyperthyroidism also cause changes in the skin that can lead to itchiness. Such changes include an increase or decrease in sweating, skin dryness and rash. The autoimmune disease, Graves’ disease occurs when the immune system attacks the thyroid gland and this leads to overproduction of thyroid hormones- Graves’ disease often manifests with skin itching symptoms.¹³

Persistent itching can also be caused by blood disorders such as Polycythemia Vera and Iron Deficiency anaemia. Polycythemia Vera is a condition where the body produces too many blood cells, which causes your blood to thicken. Patients with this condition experience itching often after a warm bath or shower.¹⁴ Iron deficiency anaemia occurs when a person has low iron levels in their blood. As well as the usual symptoms of tiredness, headaches and pale skin, anaemia patients can also experience skin itching.¹⁵

Whilst itching can be caused by changes in the skin, it can also be caused by neurological conditions that affect your nerves and their perception of pain, touch and sensation. Multiple sclerosis is one of these conditions. Multiple sclerosis occurs when a person’s immune system attacks their nerves, causing nerve malfunction that can result in poor vision, and problems with movement and balance and can for some people result in an itching sensation.¹⁶ Finally there is also a phenomenon known as a neuropathic itch. This occurs when the nerves that are responsible for detecting itches become pinched or inflamed and is seen in patients with shingles or those with chronic arthritis.¹⁷

Psychological and environmental factors

Stress is an unavoidable factor of modern-day life, however, chronic stress is widely recorded to have negative effects on physical health as well as mental health. Stress, anxiety and other mood disorders are often associated with itching and chronic itch.¹⁸ Stress is also known to exacerbate many health conditions, worsening their symptoms including exacerbating the itching caused by the conditions discussed here. Of course, this can create a vicious itch-scratch cycle that has negative consequences for both the person’s mental and physical well-being in the long term.³

Environmental conditions as previously discussed play an important role in the health of your skin barrier and disturbances to this skin barrier in whatever way, can lead to symptoms such as dryness and itching. As previously mentioned allergens and ‘triggers’ can cause significant effects on skin health by triggering allergic reactions resulting in skin rash and itching or by triggering ‘flare-ups’ of certain skin conditions such as eczema. Temperature and humidity also affect the skin's barrier. For example, temperatures that are too hot too cold or too dry will cause xerosis or dry skin that can lead to itching.⁵

Certain medications can also cause itching as a side effect. Examples of this include but are not limited to opioids, antibiotics and some chemotherapeutics.¹⁹ Itching as a side effect, although seemingly small, can really affect people's ability to stay on the medication that helps their condition. It is always advised to refer to the patient packet inserts to understand better the side effects of any medication you are taking and as always please speak to your doctor or a pharmacist if you have concerns.

Summary

Itching is a common sensation felt by many throughout their lives. Persistent itching however is an overlooked condition that causes significant irritation and mental distress to the individual. Caused by many things, including skin conditions, wider health conditions, psychological factors and environmental factors, persistent itching is a complex condition that often appears to be unexplained to the untrained eye. If itching continues for multiple weeks and you are worried please visit a pharmacist or GP for an appropriate medical consultation as there are many treatments available to help you.